Method and apparatus for in-situ chemical oxidation for soil and groundwater remediation

ABSTRACT

A method for treating groundwater and soil with a chemical oxidant, such as potassium permanganate, is provided. A chemical is placed in a powdered or pellet form into injection wells. Baffles are inserted into the ground to direct groundwater flow toward the injection wells. The groundwater flows through the injection wells to pick up the chemical oxidant. A second set of baffles are placed between the injection wells and the contaminated zone to disperse the chemical oxidant laden water. The chemical oxidant laden water flows through the contaminated field, the oxidant acting on the contaminated soil and groundwater to treat same. The injection wells can be pressurized to increase groundwater flow. Tests can be conducted on the other side of the contaminated field to measure the effectiveness of the treatment.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method and apparatus forin-situ saturated soil and groundwater remediation by chemicaloxidation, and more particularly, to a method and apparatus fordelivering an oxidant, such as potassium permanganate (KMnO₄) to acontaminated site. The KMnO₄ is solubilized into the groundwater in aninjection well and then transported through a contaminated area usingthe natural groundwater gradient.

[0003] 2. Related Art

[0004] In-situ chemical oxidation remediation techniques involvetreatment of organic contaminants by oxidizing single-chainedhydrocarbon compounds, as well as double-bonded chlorinated compounds,into carbon dioxide and water. Chemical oxidants such as Fenton'sReagent are known oxidizing agents used, in part, for groundwaterremediation. Typically, in-situ remediation using Fenton's Reagentconsists of serially injecting catalysts and reagents into thesubsurface of a contaminated site. Other oxidants such as potassiumpermanganate are known for use in water treatment plants. Additionally,it is known to inject a potassium permanganate solution into groundwaterfor groundwater remediation.

[0005] What would be desirable, but has not heretofore been provided, isa process whereby a powdered or pelletized oxidant can be placed into aninjection well, dissolved, and carried by groundwater through acontaminated soil and groundwater area for remediating same.Specifically, it would be desirable to use such a process forremediating contaminated, saturated zone soil, i.e., the soil zone belowthe water table, and groundwater.

OBJECTS AND SUMMARY OF THE INVENTION

[0006] It is an object of the present invention to provide a system forin-situ chemical oxidation of contaminated saturated zone soil andgroundwater.

[0007] It is an additional object of the present invention to provide amethod and apparatus for passively remediating contaminated saturatedzone soil and groundwater by solubilizing a chemical oxidant intogroundwater.

[0008] It is a further object of the present invention to provide amethod and apparatus for using groundwater to deliver a chemical oxidantto contaminated saturated zone soil and groundwater.

[0009] It is still a further object of the present invention to placepowder or pelletized potassium permanganate into an injection well andallow same to dissolve in groundwater flowing through the well, thegroundwater delivering the potassium permanganate to contaminatedsaturated zone soil and groundwater for remediating the contaminatedzone.

[0010] It is still a further object of the present invention to directgroundwater flow through injection wells to dissolve a chemical oxidantand carry the chemical oxidant through contaminated saturated soil forsoil and groundwater remediation.

[0011] It is even an additional object of the present invention todiffuse the flow of groundwater bearing a chemical oxidant so that theoxidant is dispersed through contaminated saturated soil and groundwaterfor remediating same.

[0012] The present invention relates to a method and apparatus fortreating contaminated groundwater and soil with a chemical oxidant, suchas potassium permanganate. More specifically, the present inventionrelates to a delivery system for delivering a chemical oxidant togroundwater for treatment of contaminated media. The chemical oxidant isplaced in a powdered or pelletized form into injection wells upstream ofthe contaminated site. Baffles may be inserted into the ground upstreamof the injection wells to channel groundwater flow toward the injectionwells. The groundwater flows through the injection wells and solubilizesa portion of the chemical oxidant. A second set of baffles may be placedbetween the injection wells and the contaminated zone to disperse thechemical oxidant laden water. The chemical oxidant laden water flowsthrough the contaminated field, the oxidant acting on the contaminatedmedia to treat same. Tests can be conducted on the other side of thecontaminated field to measure the effectiveness of the treatment. Apreferred chemical oxidant is potassium permanganate in powder or pelletform. Flow of groundwater through the wells can be increased by alteringthe natural hydraulic gradient and/or pressurizing the wells.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Other important objects and features of the invention will beapparent from the following Detailed Description of the Invention takenin connection with the accompanying drawings in which:

[0014]FIG. 1 is a cross-sectional view of an injection well withgroundwater flowing therethrough according to the present invention

[0015]FIG. 2 is a schematic diagram of groundwater directed by bafflesto flow through injection wells, then about baffles and through acontaminated area.

[0016]FIG. 3 is a detailed view of an injection well used in the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention relates to a delivery system for deliveringa chemical oxidant to groundwater for treatment of contaminated media.The oxidant is placed in a powdered or pellet form into one or moreinjection wells. Baffles may be inserted into the ground to channelgroundwater flow toward the injection wells. The groundwater flowsthrough the injection wells whereby the chemical oxidant is solubilizedinto groundwater. A second set of baffles may be used to disperse thechemical oxidant laden water. The chemical oxidant laden water flowsthrough the contaminated field, the oxidant chemically reacting with thecontaminated media to treat same. Tests can be conducted on the otherside of the contaminated field to measure the effectiveness of thetreatment. A preferred oxidant is potassium permanganate (KMnO₄), whichis manufactured by Carus Chemical Company of Peru, Ill., and sold underthe registered trademark Cairox. This oxidant is described in U.S. Pat.No. 5,152,804 dated Oct. 6, 1992 to Eissele, et al.

[0018] As shown in FIG. 1, a soil profile typically includes thefollowing layers: ground surface 9, overburden 10, silt 12, gravel 14and bedrock 16. Water, shown by arrows A, flows around baffle 20 intoinjection well 30 which contains a chemical oxidant 32 within sleeve 34.The groundwater A flows through apertures 36 in the well 30 and thesleeve 34 and becomes laden with the chemical oxidant. The water leavingthe injection well 30 is laden with the chemical oxidant as indicated byarrow B. Thereafter, the chemical oxidant laden water B is dispersed bybaffle 40 for flow through the contaminated field.

[0019] As shown in FIG. 2, water A is directed by baffles 20 throughinjection wells 30. The groundwater A picks up the chemical oxidant andleaves the injection well 30 laden with chemical oxidant as shown byarrows B. The chemical laden water B is then dispersed over a desiredarea by baffles 40 and then flows through the contaminated field 19.Typically, a concentration of 1% to 4% KMnO₄ solution is desired.

[0020] The injection wells 30 may be installed to bedrock depth using abackhoe or drilling rig as is known in the art. The wells may bescreened from the top of the bedrock to the top of the length above theseasonal high water table. The wells can be sized as desired. In anembodiment of the invention, a 24-inch diameter schedule 80 PVC pipewith 5-foot screen intervals and a 9-inch sump could be used. It may bedesirable to utilize a plurality of wells in rows. The wells could beplaced about 15 to 20 feet from each other depending on the rate ofgroundwater flow and concentration of the contamination to achieve thedesired retention time. In an embodiment of the invention, the wellshave radii of influence of 5 feet that overlap each other by 2 inches.It is to be understood, however, that various other radii of influenceand overlap factors are considered within the scope of the invention andcan be calculated using known equations to achieve a maximum delivery ofpotassium permanganate for a given treatment area.

[0021]FIG. 3 shows a detailed view of an injection well 30 of thepresent invention. The well extends from the ground surface 9 to thebedrock 16. The well can be capped with a cover 31 such as a thirty-sixinch manhole cover. The well 30 includes a well riser portion 33 whichcould be twenty-four inch diameter corrugated PVC pipe SCH 80, theheight of which will vary depending on site stratography. A screenedinterval 35 extends preferably about five feet above the bedrock 16. Thescreened interval 35 could be twenty-four inch diameter corrugated PVCSCH 80 with a 0.025 inch slot size. A sump 37 interconnects with thescreened interval 35 and is partially embedded in the bedrock 16. Thesump 37 could be nine inches and have a twenty-four inch diametercorrugated PVC pipe SCH 80 construction with an end cap. Of course,dimensions and materials can be varied to accommodate differentconditions. Wells with smaller diameters (approximately 2 inches) may beappropriate given the geologic setting. Small wells may also bedesirable if pressure needs to be increased to increase groundwaterflow, as will hereinafter be discussed.

[0022] The baffles 20 and 40 are preferably constructed of sheet pilingdriven to bedrock with a sheet-pile-driving rig. The baffles are placedat locations based on groundwater conditions and potassium permanganateloading requirements. The amount of sheet pile installed for funnelbaffles 20 depends on the thickness of the most transmissive layerwithin the impacted area, the saturated thickness, the change ingroundwater velocities, and the thickness of unsaturated soil.

[0023] The progress of the treatment, including travel time and oxidantconcentration, can be monitored through monitor and/or observationwells, which can be positioned between the injection wells 30 and thecontaminated field, within the contaminated field, and/or beyond thecontaminated field.

[0024] As is readily apparent, treatment times will vary depending upongroundwater flow rates, the contaminant mass volume, and the oxidantdemand rate at a given site. The flow of groundwater through theinjection wells can be controlled by varying the pressure differential.To accelerate the groundwater flow rate, the present invention can bemodified by pressurizing the injection wells. For example, the flow ratecan be increased by pumping air into the injection wells to force thegroundwater out. Air could be injected through a manifold with a valve.A pressure gauge could be used to monitor and maintain a desiredpressure. In another embodiment of the present invention, the injectionwell can be pressurized by introducing water into the well to increasethe hydraulic groundwater head, causing increased flow out of the well.Conversely, the gradient can be increased by lowering the gradient in adowngradient well. Advantageously, due to an increase in groundwaterflow, the delivery of potassium permanganate will also be accelerated,and treatment time reduced. In order to determine how much water or airto add to the injection well to achieve a desired increase ingroundwater flow, standard flow calculations known in the art can beused.

[0025] In order to determine the hydraulic head necessary in aninjection well to create a desired groundwater flow, and accordingly, adesired delivery of potassium permanganate, it is necessary to firstdetermine the hydraulic conductivity of the material through whichgroundwater flows without the introduction of water into the injectionwell, as well as the hydraulic gradient. This can be achieved by using astandard groundwater velocity equation listed below, in conjunction withobserved parameters: $\begin{matrix}{q = {\frac{K}{n} \times \frac{\Delta \quad H}{\Delta \quad L}}} & (1)\end{matrix}$

[0026] where q=the observed average velocity of potassium permanganate(measured in feet per day), K=the hydraulic conductivity of the materialthrough which the potassium permanganate flows (measured in feet perday), n=the porosity of the material through which the potassiumpermanganate flows (measured in percentage), ΔH=the observed change inhydraulic head between the injection well and a monitoring well(measured in feet), and ΔL=the linear distance between the injectionwell and the monitoring well (measured in feet). It is assumed, in theabove calculation, that since potassium permanganate is completelysolubilized in water and moves the same rate as the groundwater, noretardation occurs. Thus, q represents both the groundwater seepagevelocity and the rate of dispersion of potassium permanganate.

[0027] Solving for K, Equation 1 can be represented as follows:$\begin{matrix}{K = \frac{{q \cdot n \cdot \Delta}\quad L}{\Delta \quad H}} & (2)\end{matrix}$

[0028] Accordingly, using Equation 2 above, the hydraulic conductivityof the material through which potassium permanganate flows, without theintroduction of water into the injection well, can be determined. Forpurposes of illustration, the following example is provided:

[0029] Assume that potassium permanganate is observed to have moved 2.5feet in 60 days from the injection well prior to the introduction ofwater therein. Accordingly, q=2.5/60=0.041667 feet/day. Further, assumethat, based on the grain size of the aquifer, the porosity of thematerial through which the potassium permanganate moves is estimated tobe 22%. Accordingly, n=22% or 0.22. Also, assume that the distancebetween the injection well and a monitoring well is 48.75 feet;therefore, ΔL=48.75. Finally, assume that the observed change inhydraulic head between the injection well and monitoring well is 0.05feet; therefore, ΔH=0.05. Applying these observed parameters to Equation2, the hydraulic conductivity K can be determined as follows:$\begin{matrix}{K = {\frac{\left( {0.041667\quad \text{feet/day}} \right)(0.22)(48.75)}{0.05} = {8.9375\quad \text{feet/day}}}} & (3)\end{matrix}$

[0030] Thus, given the above observations, the hydraulic conductivity ofthe material through which permanganate flows, prior to the introductionof water into the injection well, is 8.9375 feet/day.

[0031] For further purposes of illustration, assume that it is desiredto increase the average velocity of potassium permanganate 1 foot/day,instead of 0.041667 feet/day, as stated above. To achieve such anincrease, the hydraulic gradient can be altered by adding water to theinjection well. Therefore, the hydraulic gradient must be determined,based upon the above-derived hydraulic conductivity of the materialthrough which potassium permanganate is presently flowing. Solving for ΔH, the required change in hydraulic head in the injection well, Equation1 can be transformed such that: $\begin{matrix}{{\Delta \quad H} = \frac{{q \cdot n \cdot \Delta}\quad L}{K}} & (4)\end{matrix}$

[0032] Accordingly, because the desired average velocity of thepotassium permanganate is 1 foot/day, q is equal to 1. K, alreadydetermined from prior observation, is equal to 8.9375 feet/day. Finally,n and ΔL, already determined, are 0.22 and 48.75, respectively. Solvingfor ΔH, the required change in hydraulic head in the injection well willbe: $\begin{matrix}{{\Delta \quad H} = {\frac{(1)(0.22)(48.75)}{8.9375} = {1.2\quad \text{feet/day}}}} & (5)\end{matrix}$

[0033] Thus, in order to increase the average velocity of potassiumpermanganate being delivered from the injection well, it is necessary tointroduce a quantity of water into the injection well that will resultin an increase of the hydraulic head of the injection of 1.2 feet.

[0034] The above calculations can also be made/verified using atwo-dimensional groundwater flow modeling program, such as the computerprogram sold under the name “WinFlow” by Environmental Simulations, Inc.

[0035] Having thus described the invention in detail, it is to beunderstood that the foregoing description is not intended to limit thespirit and scope thereof. What is desired to be protected by LettersPatent is set forth in the appended claims.

What is claimed is:
 1. A method for treating a contaminated siteincluding soil and groundwater comprising: providing one or moreinjection wells located upstream of the contaminated site in the flow ofgroundwater to the contaminated site; directing groundwater to flowthrough the one or more injection wells prior to flowing through thecontaminated site; dissolving a chemical oxidant in the groundwater asthe groundwater flows through the one or more injection wells;dispersing the groundwater with dissolved chemical oxidant for flowthrough the contaminated field; and allowing the ground water with thedissolved chemical oxidant to flow through the contaminated field, thedissolved chemical oxidant reacting with and treating the contaminatedsite.
 2. The method of claim 1 wherein the chemical oxidant is potassiumpermanganate.
 3. The method of claim 1 wherein the step of directing thewater to flow through the injection wells comprises installing firstbaffles upstream of the one or more injection wells.
 4. The method ofclaim 3 wherein the first baffles are angled to direct groundwater flowthrough the one or more injection wells.
 5. The method of claim 1further comprising monitoring the treatment by testing groundwaterdownstream of the contaminated site.
 6. The method of claim 1 whereinthe step of dispersing the groundwater with dissolved chemical oxidantcomprises installing second baffles between the one or more wells andthe contaminated site for dispersing water.
 7. The method of claim 6wherein the second baffles are oriented perpendicular to the directionof groundwater flow.
 8. The method of claim 1 further comprisingincreasing groundwater flow from the one or more wells by pressurizingthe one or more wells.
 9. The method of claim 8 wherein the one ore morewells are pressurized by injecting air into the wells.
 10. The method ofclaim 8 wherein the one or more wells are pressurized by injecting waterinto the one or more wells.
 11. An apparatus for treating a contaminatedsite including soil and groundwater comprising: at least one injectionwell positioned upstream of the contaminated site; a chemical oxidantinjected within the at least one injection well; means for directinggroundwater to flow through the at least one injection well to pick upthe chemical oxidant; and means for dispersing the groundwater withchemical oxidant to flow through contaminated site.
 12. The apparatus ofclaim 11 wherein the chemical oxidant comprises potassium permanganate.13. The apparatus of claim 12 wherein the chemical oxidant comprisespellets.
 14. The apparatus of claim 12 wherein the chemical oxidantcomprises powder.
 15. The apparatus of claim 11 wherein the means fordirecting groundwater flow through the at least one injection wellcomprises first baffles positioned upstream from the wells to funnelgroundwater flow into the wells.
 16. The apparatus of claim 15 whereinthe means for dispersing the groundwater comprises second bafflespositioned in the ground between the wells and the contaminated site.17. The apparatus of claim 16 wherein the second baffles are positionedperpendicular to the flow of groundwater.
 18. An injection well fordelivering an oxidant to a site including contaminated soil andgroundwater comprising: a sump partially embedded in bedrock; a screenedinterval interconnected with the sump; a well riser interconnected withthe screened interval and extending from the screened interval to groundsurface; and a cover positionable over the well riser.
 19. The injectionwell of claim 18 wherein the screened interval extends approximatelyfive feet from the sump.
 20. The injection well of claim 18 wherein thesump comprises a pipe with a bottom end cap.
 21. The injection well ofclaim 18 further comprising means for pressurizing the well.
 22. Theinjection well of claim 21 further comprising a pressure gauge formonitoring and maintaining pressure in the injection well.
 23. A methodfor treating a contaminated site comprising: providing an injection wellupstream of the contaminated site; introducing a solid chemical oxidantinto the injection well; allowing groundwater to flow into the injectionwell; dissolving the chemical oxidant into the groundwater; allowing thegroundwater with dissolved chemical oxidant to flow out of the injectionwell; and allowing the dissolved chemical oxidant to treat thecontaminated site.
 24. The method of claim 23, wherein the chemicaloxidant is potassium permanganate.
 25. The method of claim 24 whereinthe chemical oxidant is in pellet form.
 26. The method of claim 25wherein the chemical oxidant is in powder form.
 27. The method of claim23, further comprising: sampling the groundwater downstream of thecontaminated site; and selectively increasing or decreasing the amountof chemical oxidant in the injection well based on the results of thesampling.
 28. The method of claim 23 further comprising directing thegroundwater to flow into the injection well by installing bafflesupstream of the injection well.
 29. The method of claim 28 furthercomprising dispersing the groundwater with dissolved chemical oxidant byinstalling a second baffle between the injection well and thecontaminated site.